This invention relates generally to the field of ribbons used in printing operations such as in connection with teleprinters, wherein a type or needle of a printing head strikes the ribbon to produce printed matter on a document or the like, and more particularly to such ribbons which are continuous or ring-shaped and which are formed by connecting in fixed assembly the ends of a finite length of ribbon. Such ribbons are composed of thermoplastic synthetic material and the connection between the ends of the length of ribbon is formed by overlapping the ribbon ends and providing a welded joint between the overlapped portions.
In the construction of continuous or endless thermoplastic ribbons used in printing operations it is known to connect the ends of a finite length of ribbon by overlapping the same and gluing the overlapped portions with the aid of an interposed thermoplastic filament. The thermoplastic filament is held taut in the region of the portion thereof which is to be glued, and then the ends of the ribbon are joined by fusing the filament to the overlapped portions under conditions of pressure and heat. It is also known to connect the overlapped ends by means of an ultrasonic weld process. Continuous ribbons which are constructed in either of these two ways have a disadvantage, however, that in the region of the overlapped ribbon end portions connected by adhesion or an ultrasonically welded joint the thermoplastic material of which the ribbon is composed fills up the ink cells formed in the ribbon. Thus during a printing operation, e.g., in a teleprinter, when a type or needle of the printing head strikes against the joint in the ribbon, the application of the ink to the paper sheet or the like which is to be imprinted does not occur at all or else occurs only to an incomplete extent. Furthermore, either of these two constructions is possible only in connection with one-color ribbons. When either of such connection joints is utilized in connection with a multi-color ribbon, the colors become blurred in the region of the adhesion or welding joint. This occurs even in connection with the use of nylon fabrics, which have been widely and advantageously utilized as material for the ribbons.
A principal object of the present invention is to provide a method for constructing a continuous ribbon, having overlapped welded joints, which enjoys a high mechanical stability and strength but which also provides uninterrupted and undisturbed printing across the length of the welded joint as the joint moves past the type or needle of the printing head. Another object is to provide a multi-color ribbon having a welded joint in which the colors are maintained distinct and are not merged or blurred in the region of the welded joint. A further object is to provide a continuous ribbon having such salutary features, as well as an improved sonotrode.